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Abstract

Microﬂuidic droplet technology has been developing rapidly. However, precise control of dynamical behaviour of droplets remains a major hurdle for new designs. This study is to understand droplet deformation and breakup under simple shear ﬂow in conﬁned environment as typically found in microﬂuidic applications. In addition to the Newtonian–Newtonian system, we consider also both a Newtonian droplet in a non-Newtonian matrix ﬂuid and a non-Newtonian droplet in a Newtonian matrix. The lattice Boltzmann method is adopted to systematically investigate droplet deformation and breakup under a broad range of capillary numbers, viscosity ratios of the ﬂuids, and conﬁnement ratios considering shear-thinning and shear-thickening ﬂuids. Conﬁnement is found to enhance deformation, and the maximum deformation occurs at the viscosity ratio of unity. The droplet orients more towards the ﬂow direction with increasing viscosity ratio or conﬁnement ratio. In addition, it is noticed that the wall effect becomes more signiﬁcant for conﬁnement ratios larger than 0.4. Finally, for the whole range of Newtonian carrier ﬂuids tested, the critical capillary number above which droplet breakup occurs is only slightly affected by the conﬁnement ratio for a viscosity ratio of unity. Upon increasing the conﬁnement ratio, the critical capillary number increases for the viscosity ratios less than unity, but decreases for the viscosity ratios more than unity.
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).